EP0047678B1 - Exhaust silencer with internal resonance chamber for combustion engines - Google Patents

Description

The field concerned by this invention is that of exhaust silencers intended to equip internal combustion engines.

It is known that the exhaust noise spectra of these engines are characterized in particular by the preponderance of the serious components compared to the others (medium and acute). As soundproofing requirements become more and more stringent, the adoption of resonators incorporated into silencers has become widespread in difficult cases, knowing that only the principle of low frequency resonator (LF) Helmholtz resonator with neck or quarter d resonator is likely to face the problem of bass attenuation, whether it is preventing these serious components from contributing to the interior noise level of the vehicle or reducing the noise level of the mouth noise (noise outside).

It has therefore become common to associate, in the same silencer, several acoustic attenuation principles: reflection, interference, absorption in order to best cover the frequency range of the spectrum as a function of the relative importance of the different components. Any modern silencer intended to attenuate the components corresponding to a frequency band extending from high to low through to medium, thus has several stages of attenuation.

This is how Fig. 1 attached shows a known silencer comprising an envelope E separated by a transverse partition C into two parts: a first, located on the left in the drawing, in which are arranged the means fulfilling the functions of reflection and interference, and a second located on the right, which is the Helmholz resonator. This arrangement known for example from FR-A-2 131 431 has the drawback of shortening, for a given total length of silencer, the length of the stage with reflection and interference by the length of the resonator stage. However, it turns out that the attenuation of the components of medium frequencies whose energy lies midway between those of the bass and treble, obtained in the reflection and interference stage, is all the more effective as the length of this floor is more important.

• - La réflexion est obtenue par les jeux de perforations dont les tubes sont munis, chacune des ouvertures étant associée à la fraction correspondante de la capacité et constituant avec celle-ci un résonateur de Helmholtz élémentaire. Pour des raisons de perte de charge globale d'une part et d'efficacité acoustique d'autre part, on retient habituellement une somme d'ouvertures par tube de l'ordre de la section débitante de celui-ci. Ainsi, pour une perforation donnée, la fréquence de coupure est d'autant plus basse que la capacité traversée est plus importante, d'ou l'intérêt, pour une section de silencieux donnée, d'une longueur maximale.
• - L'interférence est obtenue par les différences de marche réalisées. La bande de fréquence intéressée par ce type d'atténuation est d'autant plus large que l'éventail des différences de marche obtenu est plus important. Compte tenu des ordres de grandeur mis en oeuvre (spectre et dimension du silencieux), les composantes moyenne fréquence (MF) sont d'autant mieux atténuées que la longueur caractéristique est plus importante.

Indeed, the floor in question consists of at least two perforated pipes crossing a capacity and whose arrangement allows two superimposing principles to be superimposed: reflection and interference.

• - The reflection is obtained by the sets of perforations with which the tubes are provided, each of the openings being associated with the corresponding fraction of the capacity and constituting therewith an elementary Helmholtz resonator. For reasons of overall pressure drop on the one hand and acoustic efficiency on the other hand, a sum of openings per tube is usually retained on the order of the flow section thereof. Thus, for a given perforation, the cutoff frequency is all the lower the higher the capacity crossed, hence the interest, for a given muffler section, of a maximum length.
• - The interference is obtained by the differences in walking achieved. The wider the frequency band interested in this type of attenuation, the wider the range of path differences obtained. Given the orders of magnitude used (spectrum and size of the silencer), the medium frequency (MF) components are all the better attenuated as the characteristic length is greater.

We also know, from FR-A-1263608 a silencer in which is incorporated a Helmholtz type resonator. However, this silencer comprises, apart from this resonator, only a succession of resonators whose speakers are arranged in series. This arrangement is cumbersome in length and does not make it possible to accommodate a reflection and / or interference stage long enough to attenuate the medium frequencies. In addition, this device results in a significant load loss due to the numerous baffles that constitute the relatively close partitions and the non-perforated tubes.

The object of this invention is therefore to provide a silencer of the type comprising a reflection and interference stage and at least one Helmholtz resonator, which, with equal total dimensions, offers improved attenuation characteristics.

To this end, it relates to an exhaust silencer for an internal combustion engine, comprising an envelope formed by a side wall and two end walls and in which are arranged at least a first reflection attenuation stage and / or interference and at least a second stage constituting a Helmholtz resonator, formed by an enclosure and a neck constituting a pressure tap communicating with the first stage, characterized in that the pressure tap of the second stage is carried out from of an end wall of the envelope by means of a neck located at least partially outside the envelope, and the enclosure of the resonator is crossed by tubes forming part of the first stage.

• la Fig. 1 représente comme on l'a déjà indiqué ci-dessus une vue en coupe développée d'un silencieux d'échappement constituant l'art antérieur;
• la Fig. 2 est est une vue analogue d'un silencieux perfectionné selon l'invention;
• la Fig. 3 est une vue également en coupe développée d'une variante; et
• les Fig. 4 et 5 sont deux vues de détail à plus grande échelle d'une partie du silencieux de la Fig. 3.

The invention will be described in more detail below with reference to the attached drawing in which:

• Fig. 1 shows, as already indicated above, a developed sectional view of an exhaust silencer constituting the prior art;
• Fig. 2 is a similar view of an improved silencer according to the invention;
• Fig. 3 is a view also in developed section of a variant; and
• Figs. 4 and 5 are two enlarged detail views of part of the silencer of FIG. 3.

The silencer of the prior art shown in FIG. Will not be described in detail. 1 which will however serve as a reference when the advantages offered by the invention are stated.

The latter, a first variant of which is shown in FIG. 2, relates to a silencer comprising a casing 1 closed at its two ends by two walls 2 and 3. Furthermore, this casing is separated by three partitions 4, 5 and 6 into four chambers respectively bearing the references 7, 8, 9 and 10. It is completed by three tubes or pipes, an inlet tube 11, an intermediate tube 12 and an outlet tube 13 which are provided, in a conventional manner, with orifices or openings as designated for example by the references 14, 15 and 16. The orifices 14 constitute, with an outer tube section 17, a high frequency resonator, the assembly of the three tubes 11, 12, 13, with their orifices and the volumes which surround them also constitute a stage d attenuation with reflection and interference.

• -en ce qui concerne l'atténuation par interférence, l'agencement suivant l'invention permet d'utiliser toute la longueur du silencieux qui, dans l'art antérieur est écourté de la longueur du volume du résonateur basse fréquence. Ceci résulte de la disposition de la prise de pression et du col de ce résonateur et au fait que la chambre 9 qui est utilisée comme capacité du résonateur basse fréquence est située dans l'étage de réflexion et d'interférence et est traversée par les tubes qui font partie de cet étage.
• en ce qui concerne l'atténuation par réflexion, l'agencement suivant l'invention permet de bénéficier, pour une même fréquence de coupure du résonateur basse fréquence, d'une capacité accrue par rapport à la disposition connue.
• en ce qui concerne le résonateur basse fréquence lui-même, l'agencement suivant l'invention permet d'accroître notablement la longueur du col sans pour autant raccourcir la longueur caractéristique de l'étage de réflexion et d'interférence, et d'abaisser la fréquence de coupure, pour un volume égal de la capacité. Par ailleurs, à fréquence de coupure et section de la capacité égales, le volume nécessaire de la capacité peur être réduit.

According to the invention, the chamber 9 which is crossed by the tubes 11, 12 and 13 constitutes a low frequency resonator or Helmholtz resonator, the pressure tap of which is located in the end wall 3, in the axial alignment of the inlet tube 11. the collar 19 of the low frequency resonator extends from the pressure outlet, and includes a curved portion 19a located outside of the envelope, and a straight portion 19 ^b which reenters inside this envelope and opens into the chamber 9 at a relatively short distance from the partition 5. If this arrangement is compared to that of FIG. 1, which represents a silencer of identical dimensions (the apparent difference in diameter between FIGS. 1 and 2 results only from the development of the section), the following advantages can be emphasized in favor of the invention:

• as regards attenuation by interference, the arrangement according to the invention makes it possible to use the entire length of the silencer which, in the prior art is shortened by the length of the volume of the low frequency resonator. This results from the arrangement of the pressure tap and the neck of this resonator and the fact that the chamber 9 which is used as the capacity of the low frequency resonator is located in the reflection and interference stage and is traversed by the tubes. which are part of this floor.
• as regards attenuation by reflection, the arrangement according to the invention makes it possible to benefit, for the same cut-off frequency of the low-frequency resonator, from an increased capacity compared to the known arrangement.
• with regard to the low frequency resonator itself, the arrangement according to the invention makes it possible to notably increase the length of the neck without shortening the characteristic length of the reflection and interference stage, and to lower the cutoff frequency, for an equal volume of capacity. Furthermore, at equal cut-off frequency and cross-section of the capacity, the necessary volume of the capacity can be reduced.

These advantages are therefore substantial, if we consider that they are obtained without modifying the size of the silencer and without increasing its cost.

• - une sourdine 49 constituant un résonateur très haute fréquence contribuant à la suppression du bruit de coupure;
• - un étage à réflexion et à interférence, haute fréquence et moyenne fréquence constitué par des orifices à persiennes 50 prévus sur les tubes 45 et 46. Un exemple de ces persiennes est représenté plus en détail aux Fig. 4 et 5;
• - un second étage à réflexion et interférence 51;
• - une perforation spéciale dite de référence, 52;
• - un étage de sortie haute fréquence 53, à réflexion ou à absorption.

The variant embodiment shown in FIG. 3 illustrates the fact that the application of the invention can be implemented in mufflers of various constructions. In this variant, the silencer comprises an envelope 31, two end walls 32, 33 and intermediate partitions 34, 35, 36, 37, 38, delimiting chambers 39, 40, 41, 42, 43, 44. Three tubes are also provided, an inlet tube 45, an intermediate tube 46 and an outlet tube 47. The low frequency resonator is here constituted by the chamber 42 and by a neck 48 extending from the wall of end 33 and constituting a pressure tap arranged in alignment with the inlet tube 45. Furthermore, the different means provided in the reflection and interference stage are as follows, considering the order of passage of the gases :

• - a mute 49 constituting a very high frequency resonator contributing to the suppression of the cut-off noise;
• a high frequency and medium frequency reflection and interference stage constituted by louver orifices 50 provided on the tubes 45 and 46. An example of these louvers is shown in more detail in FIGS. 4 and 5;
• - a second reflection and interference stage 51;
• - a special perforation called reference, 52;
• - a high frequency output stage 53, reflection or absorption.

Of course, the same advantages are obtained as in the previous example and it is very clear that the invention can be applied to these silencers of structure and construction different from those which have been shown.

Claims (4)

1. An exhaust silencer for an internal combustion engine, comprising a case formed by a lateral wall (1; 31) and two end walls (2, 3; 32, 33) and in which case are disposed at least a first reflection and/or interference attenuation stage and at least a second stage constituting a Helmholtz resonator, formed by a chamber and a neck constituting a pressure take-off communicating with the first stage, characterised in that the pressure take-off of the second stage is effected from an end wall (3; 33) of the case by means of a neck (19; 42) located at least partly outside the case, and the chamber (9; 42) of the resonator has extending therethrough pipes (11; 12, 13, 45, 46, 47) which are part of the first stage.

2. A silencer according to claim 1, characterised in that the pressure take-off the resonator is located in the end wall (3, 33) of the case opposed to the gas inlet and in alignment with an inlet pipe (11; 45).

3. A silencer according to claim 1, characterised in that the chamber (9; 42) of the resonator is disposed between two chambers (8, 10; 41, 43) which are part of the first stage.

4. A silencer according to any one of the claims 1 to 3, characterised in that the neck (19; 48) constituting the pressure take-off of the Helmholtz resonator has a curve part (19a) located outside the case and a rectilinear part (19b) which extends to the chamber (9; 42) of the resonator.

Images